1. Field
The present disclosure relates to a resin-framed membrane electrode assembly for a fuel cell.
2. Description of the Related Art
In general, a solid polymer electrolyte fuel cell includes a solid polymer electrolyte membrane, which is made from a solid polymer ion-exchange membrane. The fuel cell includes a membrane electrode assembly (MEA) in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode. Each of the anode electrode and the cathode electrode includes a catalyst layer (electrode catalyst layer) and a gas diffusion layer (porous carbon). The fuel cell further includes separators (bipolar plates) sandwiching the membrane electrode assembly therebetween. A predetermined number of such fuel cells are stacked to form a fuel cell stack, which is used, for example, as an automobile fuel cell stack.
The term “stepped MEA” refers to a type of membrane electrode assembly in which one of the gas diffusion layers has a size in plan view smaller than that of the solid polymer electrolyte membrane and the other gas diffusion layer has a size in plan view the same as that of the solid polymer electrolyte membrane. A stepped MEA is usually structured as a resin-framed stepped MEA, which has a resin frame member. This is because, by using the resin frame member, it is possible to reduce the amount of a solid polymer electrolyte membrane, which is relatively expensive, and to protect the solid polymer electrolyte membrane, which is a thin and flimsy film.
For example, Japanese Unexamined Patent Application Publication No. 2008-41337 discloses a resin-framed membrane electrode assembly including a membrane electrode assembly 1 and a resin frame 2 as illustrated in FIG. 9. The membrane electrode assembly 1 includes a polymer electrolyte membrane 3. A first electrode layer 4a and a first gas diffusion layer 4b are disposed on one side of the electrolyte membrane 3. A second electrode layer 5a and a second gas diffusion layer 5b are disposed on the other side of the electrolyte membrane 3.
The entirety of the outer peripheral edge of the first gas diffusion layer 4b is located within the outer peripheral edge of the electrolyte membrane 3. The first electrode layer 4a is disposed on a surface of the electrolyte membrane 3 in such a way that there remains a surface region of the electrolyte membrane 3 between the outer peripheral edge of the first electrode layer 4a and the outer peripheral edge of the electrolyte membrane 3 around the entire periphery of the first electrode layer 4a. The second gas diffusion layer 5b extends to at least a part of a surface of the electrolyte membrane opposite to the surface region around the entire periphery of the electrolyte membrane 3. The resin frame 2 is fixed to at least a part of the surface region.